The seed- and air-borne pathogen Colletotrichum lupini, the causal agent of lupin anthracnose, is the most important disease in white lupin (Lupinus albus) worldwide and can cause total yield loss. The aims of this study were to establish a reliable high-throughput phenotyping tool to identify anthracnose resistance in white lupin germplasm and to evaluate a genomic prediction model, accounting previously reported resistance QTLs, on a set of independent lupin genotypes. Phenotyping under controlled conditions, performing stem inoculation on seedlings, showed to be applicable for high-throughput and its disease score strongly correlated with field plot disease assessments (r = 0.95, p<0.0001) and yield (r = -0.64, p=0.035). Traditional 1-row field disease phenotyping showed no significant correlation with field plot disease assessments (r = 0.31, p=0.34) and yield (r = -0.45, p=0.17). Genomically-predicted resistance values showed no correlation with values observed under controlled or field conditions, and the parental lines of the RIL population used for constructing the prediction model exhibited a resistance pattern opposite to that displayed in the original (Australian) environment used for model construction. Differing environmental conditions, inoculation procedures or population structure may account for this result. Phenotyping a diverse set of 40 white lupin accessions under controlled conditions revealed eight accessions with improved resistance to anthracnose. The standardized area under the disease progress curves (sAUDPC) ranged from 2.1 to 2.8 compared to the susceptible reference accession with a sAUDPC of 3.85. These accessions can be incorporated into white lupin breeding programs. In conclusion, our data supports stem inoculation-based disease phenotyping under controlled conditions as a time-effective approach to identify field-relevant resistance which can now be applied to further identify sources of resistance and their underlying genetics.

Key message GWAS identifies candidate gene controlling resistance to anthracnose disease in white lupin. Abstract White lupin (Lupinus albus L.) is a promising grain legume to meet the growing demand for plant-based protein. Its cultivation, however, is severely threatened by anthracnose disease caused by the fungal pathogen Colletotrichum lupini. To dissect the genetic architecture for anthracnose resistance, genotyping by sequencing was performed on white lupin accessions collected from the center of domestication and traditional cultivation regions. GBS resulted in 4611 high-quality single-nucleotide polymorphisms (SNPs) for 181 accessions, which were combined with resistance data observed under controlled conditions to perform a genome-wide association study (GWAS). Obtained disease phenotypes were shown to highly correlate with overall three-year disease assessments under Swiss field conditions (r > 0.8). GWAS results identified two significant SNPs associated with anthracnose resistance on gene Lalb_Chr05_g0216161 encoding a RING zinc-finger E3 ubiquitin ligase which is potentially involved in plant immunity. Population analysis showed a remarkably fast linkage disequilibrium decay, weak population structure and grouping of commercial varieties with landraces, corresponding to the slow domestication history and scarcity of modern breeding efforts in white lupin. Together with 15 highly resistant accessions identified in the resistance assay, our findings show promise for further crop improvement. This study provides the basis for marker-assisted selection, genomic prediction and studies aimed at understanding anthracnose resistance mechanisms in white lupin and contributes to improving breeding programs worldwide.

White lupin (Lupinus albus) represents an important legume crop in Europe and other parts of the world due to its high protein content and potential for low-input agriculture. However, most cultivars are susceptible to anthracnose caused by Colletotrichum lupini, a seed- and air-borne fungal pathogen that causes severe yield losses. The aim of this work was to develop a C. lupini-specific quantitative real-time TaqMan PCR assay that allows for quick and reliable detection and quantification of the pathogen in infected seed and plant material. Quantification of C. lupini DNA in dry seeds allowed us to distinguish infected and certified (non-infected) seed batches with DNA loads corresponding to the disease score index and yield of the mother plants. Additionally, C. lupini DNA could be detected in infected lupin shoots and close to the infection site, thereby allowing us to study the disease cycle of this hemibiotrophic pathogen. This qPCR assay provides a useful diagnostic tool to determine anthracnose infection levels of white lupin seeds and will facilitate the use of seed health assessments as a strategy to reduce the primary infection source and spread of this disease.

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We investigated the simultaneous influence of the time of cultivation and of the osmolarity of the medium on nuclear sizes in vitro. Cells from a permanent cell line (MaTu), derived from a human breast cancer, were used. We found a linear increase of nuclear size during the first 64 h in culture. In contrast to the important influence of time on nuclear size in culture, even distinct variations of the osmolarity of the medium had little influence on nuclear size. Only if the osmolarity rose by 28% was there a clear reduction of nuclear size.